The present invention relates to a motor control system for a hoist drive according to the preamble of independent claim 1.
In order to maintain stable operation of a host drive, a rotation speed of the electric motor of the hoist drive must be limited such that the slip frequency does not exceed the pull-out slip frequency. In other words, the pull-out torque must not be reached. The pull-out torque decreases as the inverse square of the speed, so the pull-out torque is reached more easily at high speeds than at low speeds.
A prior art motor control system for a hoist drive is adapted to use load weighing data obtained from a load weighing sensor for limiting the rotation speed of the electric motor of the hoist drive. Load weighing sensors adapted to output load weighing data are relatively expensive components.